平滑的 SDL2 精灵移动答案

【问题标题】：Smooth SDL2 sprite movement平滑的 SDL2 精灵移动
【发布时间】：2020-07-08 23:32:13
【问题描述】：

我制作了一个带有视差效果的场景。我无法让精灵沿着 X 轴平滑移动。问题是不管我用SDL_RenderCopyF还是SDL_RenderCopy，慢速移动时精灵都是按照显示器的像素网格绘制的，伴随着抖动效果，当有许多层并且每个人以不同的速度移动时。

我的问题就像SDL2 Smooth texture(sprite) animation between points in time function 但是有一个版本的SDL2不支持浮点渲染，作者只好打补丁。从 2.0.10.0 版本开始，SDL 中增加了SDL_RenderCopyF、SDL_FRect 等函数，可以实现亚像素移动精灵，但在我的场景中无法使用。

FullHD 分辨率有 10 层。在 FullHD 窗口中进行渲染。

窗口和渲染初始化代码：

void CreateWidnow()
{
    var windowFlags = Settings.Fullscreen ?
        SDL.SDL_WindowFlags.SDL_WINDOW_FULLSCREEN : Settings.Resizeble ? 
        SDL.SDL_WindowFlags.SDL_WINDOW_RESIZABLE : SDL.SDL_WindowFlags.SDL_WINDOW_SHOWN;
        
    renderWindow = SDL.SDL_CreateWindow(
        Settings.DebugMode ? $"{Settings.Title} [DEBUG]" : Settings.Title, SDL.SDL_WINDOWPOS_CENTERED, 
        SDL.SDL_WINDOWPOS_CENTERED,
        Settings.Resolution.Width,
        Settings.Resolution.Height,              
        windowFlags);
}

void CreateRenderer()
{
    if(Settings.VSinc) {
        renderer = SDL.SDL_CreateRenderer(
            renderWindow, -1, 
            SDL.SDL_RendererFlags.SDL_RENDERER_PRESENTVSYNC |
            SDL.SDL_RendererFlags.SDL_RENDERER_ACCELERATED |
            SDL.SDL_RendererFlags.SDL_RENDERER_TARGETTEXTURE
        );
    }
    else
    {
        renderer = SDL.SDL_CreateRenderer(
            renderWindow, -1, 
            SDL.SDL_RendererFlags.SDL_RENDERER_ACCELERATED |
            SDL.SDL_RendererFlags.SDL_RENDERER_TARGETTEXTURE
        );
    }   
}

主循环与deltaTime的计算：

void RenderLoop()
{
    bool cap = Settings.FPS > 0;
    var timer_fps = new Timer();
        
    ulong now_counter = SDL.SDL_GetPerformanceCounter();
    ulong last_counter = 0;
    double deltaTime = 0;
        
    while (renderLoop)
    {
        timer_fps.Start();
            
        last_counter = now_counter;
        now_counter = SDL.SDL_GetPerformanceCounter();
            
        deltaTime = (double)(now_counter - last_counter) / SDL.SDL_GetPerformanceFrequency();
            
        OnPreUpdate(deltaTime);
        OnUpdate(deltaTime);
        SDL.SDL_RenderPresent(renderer);
        OnPostUpdate(deltaTime);
            
        if( ( cap ) && ( timer_fps.GetTicks() < 1000 / Settings.FPS ) )
        {
            SDL.SDL_Delay( ( 1000 / Settings.FPS  ) - timer_fps.GetTicks() );
        }
            
    }
}

Sprite 加载和渲染代码：

public Sprite(string path)
{
    Path = path;
    Transform = new Transform(new Point(0, 0));
    sprite = Image.IMG_LoadTexture(Game.RenderContext, path);
    SDL.SDL_QueryTexture(sprite, out format, out access, out width, out height); // get the width and height of the texture

    draw_rect = new SDL.SDL_FRect();
    draw_rect.w = width;
    draw_rect.h = height;
    scr_rect.x = 0; scr_rect.y = 0; scr_rect.w = width; scr_rect.h = height; 
}

public Transform Transform
{
    get; set;
}

public void Draw()
{
    draw_rect.x = (float)Transform.Position.X;
    draw_rect.y = (float)Transform.Position.Y;
    SDL.SDL_RenderCopyExF(Game.RenderContext, sprite, ref scr_rect, ref draw_rect, Transform.Degrees, IntPtr.Zero, SDL.SDL_RendererFlip.SDL_FLIP_NONE);
}

移动函数（Transform.Translate）：

public void Translate(double x, double y)
{
    position.X += x;
    position.Y += y;
}

视差实现函数（精灵离开屏幕后向右移动）：

void layerDraw(Sprite l1, Sprite l2, double speed)
{
    l1.Transform.Translate(speed, 0);
    l1.Draw();


    l2.Transform.Translate(speed, 0);
    l2.Draw();

    if (l1.Transform.Position.X <= -Settings.Resolution.Width)
        l1.Transform.SetPosition(Settings.Resolution.Width + l2.Transform.Position.X, 0);
    if (l2.Transform.Position.X <= -Settings.Resolution.Width)
        l2.Transform.SetPosition(Settings.Resolution.Width + l1.Transform.Position.X, 0);  
    }

视差渲染功能：

double speed_09 = -2.0, speed_08 = -4.0, speed_07 = -8.0, speed_06 = -16.0;
double speed_05 = -24.0, speed_04 = -32.0, speed_03 = -64.0, speed_02 = -96.0, speed_01 = -128.0;

protected override void Update(double deltaTime)
{
    background.Draw();
    layerDraw(forest_091, forest_092, speed_09 * deltaTime);
    layerDraw(forest_081, forest_082, speed_08 * deltaTime);
    layerDraw(forest_071, forest_072, speed_07 * deltaTime);
    layerDraw(forest_061, forest_062, speed_06 * deltaTime);
    layerDraw(particles051, particles052, speed_05 * deltaTime);
    layerDraw(forest_041, forest_042, speed_04 * deltaTime);
    layerDraw(particles_031, particles_032, speed_03 * deltaTime);
    layerDraw(bushes_021, bushes_022, speed_02 * deltaTime);
    layerDraw(mist_011, mist_012, speed_01 * deltaTime);
}

将forest_091 坐标输出到控制台：

[11:31:07:32] (x,y): = (1902,7461329999965:0), deltaTime = 0,001391, speed = -0,002782
[11:31:07:32] (x:y): = (1902,7430913999965:0), deltaTime = 0,0015208, speed = -0,0030416
[11:31:07:32] (x:y): = (1902,7400399999965:0), deltaTime = 0,0015257, speed = -0,0030514
[11:31:07:32] (x:y): = (1902,7370409999965:0), deltaTime = 0,0014995, speed = -0,002999
[11:31:07:32] (x:y): = (1902,7339605999964:0), deltaTime = 0,0015402, speed = -0,0030804
[11:31:07:33] (x:y): = (1902,7300727999964:0), deltaTime = 0,0019439, speed = -0,0038878
[11:31:07:33] (x:y): = (1902,7271281999963:0), deltaTime = 0,0014723, speed = -0,0029446
[11:31:07:33] (x:y): = (1902,7241953999962:0), deltaTime = 0,0014664, speed = -0,0029328
[11:31:07:33] (x:y): = (1902,7212207999962:0), deltaTime = 0,0014873, speed = -0,0029746
[11:31:07:33] (x:y): = (1902,7181395999962:0), deltaTime = 0,0015406, speed = -0,0030812
[11:31:07:33] (x:y): = (1902,715346599996:0), deltaTime = 0,0013965, speed = -0,002793
[11:31:07:33] (x:y): = (1902,712221399996:0), deltaTime = 0,0015626, speed = -0,0031252
[11:31:07:34] (x:y): = (1902,709382799996:0), deltaTime = 0,0014193, speed = -0,0028386

Link to youtube with a demonstration of the problemы

我使用 nectcore3.1，SDL2-CS и SDL2 v2.0.10.0

UPD：记录 deltaTime 计算：

[08:48:34:25] now_counter = 1097310517365, last_counter = 1097310516099, now_counter-last_counter = 1266
[08:48:34:25] now_counter = 1097310519141, last_counter = 1097310517365, now_counter-last_counter = 1776
[08:48:34:25] now_counter = 1097310521406, last_counter = 1097310519141, now_counter-last_counter = 2265
[08:48:34:25] now_counter = 1097310532746, last_counter = 1097310521406, now_counter-last_counter = 11340
[08:48:34:25] now_counter = 1097310534069, last_counter = 1097310532746, now_counter-last_counter = 1323
[08:48:34:25] now_counter = 1097310535356, last_counter = 1097310534069, now_counter-last_counter = 1287
[08:48:34:25] now_counter = 1097310536628, last_counter = 1097310535356, now_counter-last_counter = 1272
[08:48:34:25] now_counter = 1097310537897, last_counter = 1097310536628, now_counter-last_counter = 1269
[08:48:34:25] now_counter = 1097310539169, last_counter = 1097310537897, now_counter-last_counter = 1272
[08:48:34:25] now_counter = 1097310540441, last_counter = 1097310539169, now_counter-last_counter = 1272`

【问题讨论】：

您能否将计时器的整数值也添加到日志中？ now_counter - last_counter 或只是 now_counter。
@keltar 发布更新
抱歉，只有浮点数和整数值都显示在同一个日志中才有意义，所以我将解释为什么我要求它。我的猜测是您的加法计算累积了不精确性，因此您的增量运动总和与预期结果不同。我总是尽可能推荐整数计算；更简单的解决方案可能是使用总通过时间而不是 dt（并在 2 小时左右翻转以避免精度损失峰值）。

标签： c# .net-core sdl-2

【解决方案1】：

感谢keltar 的回答和花费的时间。其实我也为解决这个问题苦苦挣扎了很久，真心不明白为什么在SDL2中加入了绘制浮点精灵的能力后，他们还是按照显示器的像素网格来绘制我的。

好消息：deltaTime 计算正确，并且在将坐标传输到 SDL 渲染时，舍入双精度没有问题！

坏消息：解决方案太简单了，花几天时间就可以了。

SDL.SDL_SetHint (SDL.SDL_HINT_RENDER_SCALE_QUALITY, "2");

这一行告诉 SDL2 在渲染精灵时使用各向异性过滤。它使我的动画流畅。

【讨论】：